/*
 * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
 * or more contributor license agreements. Licensed under the Elastic License
 * 2.0 and the Server Side Public License, v 1; you may not use this file except
 * in compliance with, at your election, the Elastic License 2.0 or the Server
 * Side Public License, v 1.
 */

package org.elasticsearch.action.search;

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import org.elasticsearch.ExceptionsHelper;
import org.elasticsearch.TransportVersions;
import org.elasticsearch.action.ActionListener;
import org.elasticsearch.action.ActionListenerResponseHandler;
import org.elasticsearch.action.ActionType;
import org.elasticsearch.action.IndicesRequest;
import org.elasticsearch.action.OriginalIndices;
import org.elasticsearch.action.RemoteClusterActionType;
import org.elasticsearch.action.ResolvedIndices;
import org.elasticsearch.action.ShardOperationFailedException;
import org.elasticsearch.action.admin.cluster.shards.ClusterSearchShardsRequest;
import org.elasticsearch.action.admin.cluster.shards.ClusterSearchShardsResponse;
import org.elasticsearch.action.admin.cluster.shards.TransportClusterSearchShardsAction;
import org.elasticsearch.action.admin.cluster.stats.CCSUsage;
import org.elasticsearch.action.admin.cluster.stats.CCSUsageTelemetry;
import org.elasticsearch.action.support.ActionFilters;
import org.elasticsearch.action.support.HandledTransportAction;
import org.elasticsearch.action.support.IndicesOptions;
import org.elasticsearch.action.support.master.MasterNodeRequest;
import org.elasticsearch.client.internal.Client;
import org.elasticsearch.cluster.ClusterState;
import org.elasticsearch.cluster.block.ClusterBlockException;
import org.elasticsearch.cluster.block.ClusterBlockLevel;
import org.elasticsearch.cluster.metadata.IndexAbstraction;
import org.elasticsearch.cluster.metadata.IndexMetadata;
import org.elasticsearch.cluster.metadata.IndexNameExpressionResolver;
import org.elasticsearch.cluster.node.DiscoveryNode;
import org.elasticsearch.cluster.node.DiscoveryNodes;
import org.elasticsearch.cluster.routing.GroupShardsIterator;
import org.elasticsearch.cluster.routing.OperationRouting;
import org.elasticsearch.cluster.routing.ShardIterator;
import org.elasticsearch.cluster.routing.ShardRouting;
import org.elasticsearch.cluster.service.ClusterService;
import org.elasticsearch.common.Strings;
import org.elasticsearch.common.breaker.CircuitBreaker;
import org.elasticsearch.common.io.stream.NamedWriteableRegistry;
import org.elasticsearch.common.logging.DeprecationCategory;
import org.elasticsearch.common.logging.DeprecationLogger;
import org.elasticsearch.common.regex.Regex;
import org.elasticsearch.common.settings.Setting;
import org.elasticsearch.common.settings.Setting.Property;
import org.elasticsearch.common.util.ArrayUtils;
import org.elasticsearch.common.util.CollectionUtils;
import org.elasticsearch.common.util.FeatureFlag;
import org.elasticsearch.common.util.Maps;
import org.elasticsearch.common.util.concurrent.CountDown;
import org.elasticsearch.common.util.concurrent.EsExecutors;
import org.elasticsearch.core.Predicates;
import org.elasticsearch.core.TimeValue;
import org.elasticsearch.index.Index;
import org.elasticsearch.index.IndexNotFoundException;
import org.elasticsearch.index.query.QueryBuilder;
import org.elasticsearch.index.query.Rewriteable;
import org.elasticsearch.index.shard.ShardId;
import org.elasticsearch.index.shard.ShardNotFoundException;
import org.elasticsearch.indices.ExecutorSelector;
import org.elasticsearch.indices.breaker.CircuitBreakerService;
import org.elasticsearch.injection.guice.Inject;
import org.elasticsearch.rest.action.search.SearchResponseMetrics;
import org.elasticsearch.search.SearchPhaseResult;
import org.elasticsearch.search.SearchService;
import org.elasticsearch.search.aggregations.AggregationReduceContext;
import org.elasticsearch.search.builder.PointInTimeBuilder;
import org.elasticsearch.search.builder.SearchSourceBuilder;
import org.elasticsearch.search.internal.AliasFilter;
import org.elasticsearch.search.internal.SearchContext;
import org.elasticsearch.search.profile.SearchProfileResults;
import org.elasticsearch.search.profile.SearchProfileShardResult;
import org.elasticsearch.tasks.Task;
import org.elasticsearch.tasks.TaskId;
import org.elasticsearch.threadpool.ThreadPool;
import org.elasticsearch.transport.RemoteClusterAware;
import org.elasticsearch.transport.RemoteClusterService;
import org.elasticsearch.transport.RemoteTransportException;
import org.elasticsearch.transport.Transport;
import org.elasticsearch.transport.TransportRequestOptions;
import org.elasticsearch.transport.TransportService;
import org.elasticsearch.usage.UsageService;
import org.elasticsearch.xcontent.ToXContent;
import org.elasticsearch.xcontent.XContentFactory;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.Executor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicReference;
import java.util.function.BiConsumer;
import java.util.function.BiFunction;
import java.util.function.Function;
import java.util.function.LongSupplier;

import static org.elasticsearch.action.search.SearchType.DFS_QUERY_THEN_FETCH;
import static org.elasticsearch.action.search.SearchType.QUERY_THEN_FETCH;
import static org.elasticsearch.action.search.TransportSearchHelper.checkCCSVersionCompatibility;
import static org.elasticsearch.search.sort.FieldSortBuilder.hasPrimaryFieldSort;
import static org.elasticsearch.threadpool.ThreadPool.Names.SYSTEM_CRITICAL_READ;
import static org.elasticsearch.threadpool.ThreadPool.Names.SYSTEM_READ;

public class TransportSearchAction extends HandledTransportAction<SearchRequest, SearchResponse> {

    public static final String NAME = "indices:data/read/search";
    public static final ActionType<SearchResponse> TYPE = new ActionType<>(NAME);
    public static final RemoteClusterActionType<SearchResponse> REMOTE_TYPE = new RemoteClusterActionType<>(NAME, SearchResponse::new);
    private static final Logger logger = LogManager.getLogger(TransportSearchAction.class);
    private static final DeprecationLogger DEPRECATION_LOGGER = DeprecationLogger.getLogger(TransportSearchAction.class);
    public static final String FROZEN_INDICES_DEPRECATION_MESSAGE = "Searching frozen indices [{}] is deprecated."
        + " Consider cold or frozen tiers in place of frozen indices. The frozen feature will be removed in a feature release.";

    private static final FeatureFlag CCS_TELEMETRY_FEATURE_FLAG = new FeatureFlag("ccs_telemetry");

    /** The maximum number of shards for a single search request. */
    public static final Setting<Long> SHARD_COUNT_LIMIT_SETTING = Setting.longSetting(
        "action.search.shard_count.limit",
        Long.MAX_VALUE,
        1L,
        Property.Dynamic,
        Property.NodeScope
    );

    public static final Setting<Integer> DEFAULT_PRE_FILTER_SHARD_SIZE = Setting.intSetting(
        "action.search.pre_filter_shard_size.default",
        SearchRequest.DEFAULT_PRE_FILTER_SHARD_SIZE,
        1,
        Property.NodeScope
    );

    private final ThreadPool threadPool;
    private final ClusterService clusterService;
    private final TransportService transportService;
    private final SearchTransportService searchTransportService;
    private final RemoteClusterService remoteClusterService;
    private final SearchPhaseController searchPhaseController;
    private final SearchService searchService;
    private final IndexNameExpressionResolver indexNameExpressionResolver;
    private final NamedWriteableRegistry namedWriteableRegistry;
    private final CircuitBreaker circuitBreaker;
    private final ExecutorSelector executorSelector;
    private final int defaultPreFilterShardSize;
    private final boolean ccsCheckCompatibility;
    private final SearchResponseMetrics searchResponseMetrics;
    private final Client client;
    private final UsageService usageService;

    @Inject
    public TransportSearchAction(
        ThreadPool threadPool,
        CircuitBreakerService circuitBreakerService,
        TransportService transportService,
        SearchService searchService,
        SearchTransportService searchTransportService,
        SearchPhaseController searchPhaseController,
        ClusterService clusterService,
        ActionFilters actionFilters,
        IndexNameExpressionResolver indexNameExpressionResolver,
        NamedWriteableRegistry namedWriteableRegistry,
        ExecutorSelector executorSelector,
        SearchTransportAPMMetrics searchTransportMetrics,
        SearchResponseMetrics searchResponseMetrics,
        Client client,
        UsageService usageService
    ) {
        super(TYPE.name(), transportService, actionFilters, SearchRequest::new, EsExecutors.DIRECT_EXECUTOR_SERVICE);
        this.threadPool = threadPool;
        this.circuitBreaker = circuitBreakerService.getBreaker(CircuitBreaker.REQUEST);
        this.searchPhaseController = searchPhaseController;
        this.searchTransportService = searchTransportService;
        this.remoteClusterService = searchTransportService.getRemoteClusterService();
        SearchTransportService.registerRequestHandler(transportService, searchService, searchTransportMetrics);
        this.clusterService = clusterService;
        this.transportService = transportService;
        this.searchService = searchService;
        this.indexNameExpressionResolver = indexNameExpressionResolver;
        this.namedWriteableRegistry = namedWriteableRegistry;
        this.executorSelector = executorSelector;
        this.defaultPreFilterShardSize = DEFAULT_PRE_FILTER_SHARD_SIZE.get(clusterService.getSettings());
        this.ccsCheckCompatibility = SearchService.CCS_VERSION_CHECK_SETTING.get(clusterService.getSettings());
        this.searchResponseMetrics = searchResponseMetrics;
        this.client = client;
        this.usageService = usageService;
    }

    private Map<String, OriginalIndices> buildPerIndexOriginalIndices(
        ClusterState clusterState,
        Set<String> indicesAndAliases,
        String[] indices,
        IndicesOptions indicesOptions
    ) {
        Map<String, OriginalIndices> res = Maps.newMapWithExpectedSize(indices.length);
        var blocks = clusterState.blocks();
        // optimization: mostly we do not have any blocks so there's no point in the expensive per-index checking
        boolean hasBlocks = blocks.global().isEmpty() == false || blocks.indices().isEmpty() == false;
        for (String index : indices) {
            if (hasBlocks) {
                blocks.indexBlockedRaiseException(ClusterBlockLevel.READ, index);
            }

            String[] aliases = indexNameExpressionResolver.indexAliases(
                clusterState,
                index,
                Predicates.always(),
                Predicates.always(),
                true,
                indicesAndAliases
            );
            String[] finalIndices = Strings.EMPTY_ARRAY;
            if (aliases == null
                || aliases.length == 0
                || indicesAndAliases.contains(index)
                || hasDataStreamRef(clusterState, indicesAndAliases, index)) {
                finalIndices = new String[] { index };
            }
            if (aliases != null) {
                finalIndices = finalIndices.length == 0 ? aliases : ArrayUtils.concat(finalIndices, aliases);
            }
            res.put(index, new OriginalIndices(finalIndices, indicesOptions));
        }
        return res;
    }

    private static boolean hasDataStreamRef(ClusterState clusterState, Set<String> indicesAndAliases, String index) {
        IndexAbstraction ret = clusterState.getMetadata().getIndicesLookup().get(index);
        if (ret == null || ret.getParentDataStream() == null) {
            return false;
        }
        return indicesAndAliases.contains(ret.getParentDataStream().getName());
    }

    Map<String, AliasFilter> buildIndexAliasFilters(ClusterState clusterState, Set<String> indicesAndAliases, Index[] concreteIndices) {
        final Map<String, AliasFilter> aliasFilterMap = new HashMap<>();
        for (Index index : concreteIndices) {
            clusterState.blocks().indexBlockedRaiseException(ClusterBlockLevel.READ, index.getName());
            AliasFilter aliasFilter = searchService.buildAliasFilter(clusterState, index.getName(), indicesAndAliases);
            assert aliasFilter != null;
            aliasFilterMap.put(index.getUUID(), aliasFilter);
        }
        return aliasFilterMap;
    }

    private Map<String, Float> resolveIndexBoosts(SearchRequest searchRequest, ClusterState clusterState) {
        if (searchRequest.source() == null) {
            return Collections.emptyMap();
        }

        SearchSourceBuilder source = searchRequest.source();
        if (source.indexBoosts() == null) {
            return Collections.emptyMap();
        }

        Map<String, Float> concreteIndexBoosts = new HashMap<>();
        for (SearchSourceBuilder.IndexBoost ib : source.indexBoosts()) {
            Index[] concreteIndices = indexNameExpressionResolver.concreteIndices(
                clusterState,
                searchRequest.indicesOptions(),
                ib.getIndex()
            );

            for (Index concreteIndex : concreteIndices) {
                concreteIndexBoosts.putIfAbsent(concreteIndex.getUUID(), ib.getBoost());
            }
        }
        return Collections.unmodifiableMap(concreteIndexBoosts);
    }

    /**
     * Search operations need two clocks. One clock is to fulfill real clock needs (e.g., resolving
     * "now" to an index name). Another clock is needed for measuring how long a search operation
     * took. These two uses are at odds with each other. There are many issues with using a real
     * clock for measuring how long an operation took (they often lack precision, they are subject
     * to moving backwards due to NTP and other such complexities, etc.). There are also issues with
     * using a relative clock for reporting real time. Thus, we simply separate these two uses.
     */
    public record SearchTimeProvider(long absoluteStartMillis, long relativeStartNanos, LongSupplier relativeCurrentNanosProvider) {

        /**
         * Instantiates a new search time provider. The absolute start time is the real clock time
         * used for resolving index expressions that include dates. The relative start time is the
         * start of the search operation according to a relative clock. The total time the search
         * operation took can be measured against the provided relative clock and the relative start
         * time.
         *
         * @param absoluteStartMillis          the absolute start time in milliseconds since the epoch
         * @param relativeStartNanos           the relative start time in nanoseconds
         * @param relativeCurrentNanosProvider provides the current relative time
         */
        public SearchTimeProvider {}

        public long buildTookInMillis() {
            return TimeUnit.NANOSECONDS.toMillis(relativeCurrentNanosProvider.getAsLong() - relativeStartNanos);
        }
    }

    @Override
    protected void doExecute(Task task, SearchRequest searchRequest, ActionListener<SearchResponse> listener) {
        ActionListener<SearchResponse> loggingAndMetrics = new SearchResponseActionListener((SearchTask) task, listener);
        executeRequest((SearchTask) task, searchRequest, loggingAndMetrics, AsyncSearchActionProvider::new);
    }

    void executeRequest(
        SearchTask task,
        SearchRequest original,
        ActionListener<SearchResponse> listener,
        Function<ActionListener<SearchResponse>, SearchPhaseProvider> searchPhaseProvider
    ) {
        final long relativeStartNanos = System.nanoTime();
        final SearchTimeProvider timeProvider = new SearchTimeProvider(
            original.getOrCreateAbsoluteStartMillis(),
            relativeStartNanos,
            System::nanoTime
        );

        final ClusterState clusterState = clusterService.state();
        clusterState.blocks().globalBlockedRaiseException(ClusterBlockLevel.READ);

        final ResolvedIndices resolvedIndices;
        if (original.pointInTimeBuilder() != null) {
            resolvedIndices = ResolvedIndices.resolveWithPIT(
                original.pointInTimeBuilder(),
                original.indicesOptions(),
                clusterState,
                namedWriteableRegistry
            );
        } else {
            resolvedIndices = ResolvedIndices.resolveWithIndicesRequest(
                original,
                clusterState,
                indexNameExpressionResolver,
                remoteClusterService,
                timeProvider.absoluteStartMillis()
            );
            frozenIndexCheck(resolvedIndices);
        }

        ActionListener<SearchRequest> rewriteListener = listener.delegateFailureAndWrap((delegate, rewritten) -> {
            if (ccsCheckCompatibility) {
                checkCCSVersionCompatibility(rewritten);
            }

            if (resolvedIndices.getRemoteClusterIndices().isEmpty()) {
                executeLocalSearch(
                    task,
                    timeProvider,
                    rewritten,
                    resolvedIndices,
                    clusterState,
                    SearchResponse.Clusters.EMPTY,
                    searchPhaseProvider.apply(delegate)
                );
            } else {
                if ((listener instanceof TelemetryListener tl) && CCS_TELEMETRY_FEATURE_FLAG.isEnabled()) {
                    tl.setRemotes(resolvedIndices.getRemoteClusterIndices().size());
                    if (task.isAsync()) {
                        tl.setFeature(CCSUsageTelemetry.ASYNC_FEATURE);
                    }
                    String client = task.getHeader(Task.X_ELASTIC_PRODUCT_ORIGIN_HTTP_HEADER);
                    if (client != null) {
                        tl.setClient(client);
                    }
                    // Check if any of the index patterns are wildcard patterns
                    var localIndices = resolvedIndices.getLocalIndices();
                    if (localIndices != null && Arrays.stream(localIndices.indices()).anyMatch(Regex::isSimpleMatchPattern)) {
                        tl.setFeature(CCSUsageTelemetry.WILDCARD_FEATURE);
                    }
                    if (resolvedIndices.getRemoteClusterIndices()
                        .values()
                        .stream()
                        .anyMatch(indices -> Arrays.stream(indices.indices()).anyMatch(Regex::isSimpleMatchPattern))) {
                        tl.setFeature(CCSUsageTelemetry.WILDCARD_FEATURE);
                    }
                }
                final TaskId parentTaskId = task.taskInfo(clusterService.localNode().getId(), false).taskId();
                if (shouldMinimizeRoundtrips(rewritten)) {
                    if ((listener instanceof TelemetryListener tl) && CCS_TELEMETRY_FEATURE_FLAG.isEnabled()) {
                        tl.setFeature(CCSUsageTelemetry.MRT_FEATURE);
                    }
                    final AggregationReduceContext.Builder aggregationReduceContextBuilder = rewritten.source() != null
                        && rewritten.source().aggregations() != null
                            ? searchService.aggReduceContextBuilder(task::isCancelled, rewritten.source().aggregations())
                            : null;
                    SearchResponse.Clusters clusters = new SearchResponse.Clusters(
                        resolvedIndices.getLocalIndices(),
                        resolvedIndices.getRemoteClusterIndices(),
                        true,
                        remoteClusterService::isSkipUnavailable
                    );
                    if (resolvedIndices.getLocalIndices() == null) {
                        // Notify the progress listener that a CCS with minimize_roundtrips is happening remote-only (no local shards)
                        task.getProgressListener()
                            .notifyListShards(Collections.emptyList(), Collections.emptyList(), clusters, false, timeProvider);
                    }
                    ccsRemoteReduce(
                        task,
                        parentTaskId,
                        rewritten,
                        resolvedIndices,
                        clusters,
                        timeProvider,
                        aggregationReduceContextBuilder,
                        remoteClusterService,
                        threadPool,
                        delegate,
                        (r, l) -> executeLocalSearch(
                            task,
                            timeProvider,
                            r,
                            resolvedIndices,
                            clusterState,
                            clusters,
                            searchPhaseProvider.apply(l)
                        )
                    );
                } else {
                    final SearchContextId searchContext = resolvedIndices.getSearchContextId();
                    SearchResponse.Clusters clusters = new SearchResponse.Clusters(
                        resolvedIndices.getLocalIndices(),
                        resolvedIndices.getRemoteClusterIndices(),
                        false,
                        remoteClusterService::isSkipUnavailable
                    );

                    // TODO: pass parentTaskId
                    collectSearchShards(
                        rewritten.indicesOptions(),
                        rewritten.preference(),
                        rewritten.routing(),
                        rewritten.source() != null ? rewritten.source().query() : null,
                        Objects.requireNonNullElse(rewritten.allowPartialSearchResults(), searchService.defaultAllowPartialSearchResults()),
                        searchContext,
                        resolvedIndices.getRemoteClusterIndices(),
                        clusters,
                        timeProvider,
                        transportService,
                        delegate.delegateFailureAndWrap((finalDelegate, searchShardsResponses) -> {
                            final BiFunction<String, String, DiscoveryNode> clusterNodeLookup = getRemoteClusterNodeLookup(
                                searchShardsResponses
                            );
                            final Map<String, AliasFilter> remoteAliasFilters;
                            final List<SearchShardIterator> remoteShardIterators;
                            if (searchContext != null) {
                                remoteAliasFilters = searchContext.aliasFilter();
                                remoteShardIterators = getRemoteShardsIteratorFromPointInTime(
                                    searchShardsResponses,
                                    searchContext,
                                    rewritten.pointInTimeBuilder().getKeepAlive(),
                                    resolvedIndices.getRemoteClusterIndices()
                                );
                            } else {
                                remoteAliasFilters = new HashMap<>();
                                for (SearchShardsResponse searchShardsResponse : searchShardsResponses.values()) {
                                    remoteAliasFilters.putAll(searchShardsResponse.getAliasFilters());
                                }
                                remoteShardIterators = getRemoteShardsIterator(
                                    searchShardsResponses,
                                    resolvedIndices.getRemoteClusterIndices(),
                                    remoteAliasFilters
                                );
                            }
                            executeSearch(
                                task,
                                timeProvider,
                                rewritten,
                                resolvedIndices,
                                remoteShardIterators,
                                clusterNodeLookup,
                                clusterState,
                                remoteAliasFilters,
                                clusters,
                                searchPhaseProvider.apply(finalDelegate)
                            );
                        })
                    );
                }
            }
        });
        final SearchSourceBuilder source = original.source();
        if (shouldOpenPIT(source)) {
            openPIT(client, original, searchService.getDefaultKeepAliveInMillis(), listener.delegateFailureAndWrap((delegate, resp) -> {
                // We set the keep alive to -1 to indicate that we don't need the pit id in the response.
                // This is needed since we delete the pit prior to sending the response so the id doesn't exist anymore.
                source.pointInTimeBuilder(new PointInTimeBuilder(resp.getPointInTimeId()).setKeepAlive(TimeValue.MINUS_ONE));
                executeRequest(task, original, new ActionListener<>() {
                    @Override
                    public void onResponse(SearchResponse response) {
                        // we need to close the PIT first so we delay the release of the response to after the closing
                        response.incRef();
                        closePIT(
                            client,
                            original.source().pointInTimeBuilder(),
                            () -> ActionListener.respondAndRelease(listener, response)
                        );
                    }

                    @Override
                    public void onFailure(Exception e) {
                        closePIT(client, original.source().pointInTimeBuilder(), () -> listener.onFailure(e));
                    }
                }, searchPhaseProvider);
            }));
        } else {
            Rewriteable.rewriteAndFetch(
                original,
                searchService.getRewriteContext(timeProvider::absoluteStartMillis, resolvedIndices, original.pointInTimeBuilder()),
                rewriteListener
            );
        }
    }

    /**
     * Returns true if the provided source needs to open a shared point in time prior to executing the request.
     */
    private boolean shouldOpenPIT(SearchSourceBuilder source) {
        if (source == null) {
            return false;
        }
        if (source.pointInTimeBuilder() != null) {
            return false;
        }
        var retriever = source.retriever();
        return retriever != null && retriever.isCompound();
    }

    static void openPIT(Client client, SearchRequest request, long keepAliveMillis, ActionListener<OpenPointInTimeResponse> listener) {
        OpenPointInTimeRequest pitReq = new OpenPointInTimeRequest(request.indices()).indicesOptions(request.indicesOptions())
            .preference(request.preference())
            .routing(request.routing())
            .keepAlive(TimeValue.timeValueMillis(keepAliveMillis));
        client.execute(TransportOpenPointInTimeAction.TYPE, pitReq, listener);
    }

    static void closePIT(Client client, PointInTimeBuilder pit, Runnable next) {
        client.execute(
            TransportClosePointInTimeAction.TYPE,
            new ClosePointInTimeRequest(pit.getEncodedId()),
            ActionListener.runAfter(new ActionListener<>() {
                @Override
                public void onResponse(ClosePointInTimeResponse closePointInTimeResponse) {}

                @Override
                public void onFailure(Exception e) {}
            }, next)
        );
    }

    static void adjustSearchType(SearchRequest searchRequest, boolean singleShard) {
        // if there's a kNN search, always use DFS_QUERY_THEN_FETCH
        if (searchRequest.hasKnnSearch()) {
            searchRequest.searchType(DFS_QUERY_THEN_FETCH);
            return;
        }

        // if there's only suggest, disable request cache and always use QUERY_THEN_FETCH
        if (searchRequest.isSuggestOnly()) {
            searchRequest.requestCache(false);
            searchRequest.searchType(QUERY_THEN_FETCH);
            return;
        }

        // optimize search type for cases where there is only one shard group to search on
        if (singleShard) {
            // if we only have one group, then we always want Q_T_F, no need for DFS, and no need to do THEN since we hit one shard
            searchRequest.searchType(QUERY_THEN_FETCH);
        }
    }

    public static boolean shouldMinimizeRoundtrips(SearchRequest searchRequest) {
        if (searchRequest.isCcsMinimizeRoundtrips() == false) {
            return false;
        }
        if (searchRequest.scroll() != null) {
            return false;
        }
        if (searchRequest.pointInTimeBuilder() != null) {
            return false;
        }
        if (searchRequest.searchType() == DFS_QUERY_THEN_FETCH) {
            return false;
        }
        if (searchRequest.hasKnnSearch()) {
            return false;
        }
        SearchSourceBuilder source = searchRequest.source();
        return source == null
            || source.collapse() == null
            || source.collapse().getInnerHits() == null
            || source.collapse().getInnerHits().isEmpty();
    }

    /**
     * Handles ccs_minimize_roundtrips=true
     */
    static void ccsRemoteReduce(
        SearchTask task,
        TaskId parentTaskId,
        SearchRequest searchRequest,
        ResolvedIndices resolvedIndices,
        SearchResponse.Clusters clusters,
        SearchTimeProvider timeProvider,
        AggregationReduceContext.Builder aggReduceContextBuilder,
        RemoteClusterService remoteClusterService,
        ThreadPool threadPool,
        ActionListener<SearchResponse> listener,
        BiConsumer<SearchRequest, ActionListener<SearchResponse>> localSearchConsumer
    ) {
        final var remoteClientResponseExecutor = threadPool.executor(ThreadPool.Names.SEARCH_COORDINATION);
        if (resolvedIndices.getLocalIndices() == null && resolvedIndices.getRemoteClusterIndices().size() == 1) {
            // if we are searching against a single remote cluster, we simply forward the original search request to such cluster
            // and we directly perform final reduction in the remote cluster
            Map.Entry<String, OriginalIndices> entry = resolvedIndices.getRemoteClusterIndices().entrySet().iterator().next();
            String clusterAlias = entry.getKey();
            boolean skipUnavailable = remoteClusterService.isSkipUnavailable(clusterAlias);
            OriginalIndices indices = entry.getValue();
            SearchRequest ccsSearchRequest = SearchRequest.subSearchRequest(
                parentTaskId,
                searchRequest,
                indices.indices(),
                clusterAlias,
                timeProvider.absoluteStartMillis(),
                true
            );
            var remoteClusterClient = remoteClusterService.getRemoteClusterClient(
                clusterAlias,
                remoteClientResponseExecutor,
                RemoteClusterService.DisconnectedStrategy.RECONNECT_UNLESS_SKIP_UNAVAILABLE
            );
            remoteClusterClient.execute(TransportSearchAction.REMOTE_TYPE, ccsSearchRequest, new ActionListener<>() {
                @Override
                public void onResponse(SearchResponse searchResponse) {
                    // overwrite the existing cluster entry with the updated one
                    ccsClusterInfoUpdate(searchResponse, clusters, clusterAlias, skipUnavailable);
                    Map<String, SearchProfileShardResult> profileResults = searchResponse.getProfileResults();
                    SearchProfileResults profile = profileResults == null || profileResults.isEmpty()
                        ? null
                        : new SearchProfileResults(profileResults);

                    ActionListener.respondAndRelease(
                        listener,
                        new SearchResponse(
                            searchResponse.getHits(),
                            searchResponse.getAggregations(),
                            searchResponse.getSuggest(),
                            searchResponse.isTimedOut(),
                            searchResponse.isTerminatedEarly(),
                            profile,
                            searchResponse.getNumReducePhases(),
                            searchResponse.getScrollId(),
                            searchResponse.getTotalShards(),
                            searchResponse.getSuccessfulShards(),
                            searchResponse.getSkippedShards(),
                            timeProvider.buildTookInMillis(),
                            searchResponse.getShardFailures(),
                            clusters,
                            searchResponse.pointInTimeId()
                        )
                    );
                }

                @Override
                public void onFailure(Exception e) {
                    ShardSearchFailure failure = new ShardSearchFailure(e);
                    logCCSError(failure, clusterAlias, skipUnavailable);
                    ccsClusterInfoUpdate(failure, clusters, clusterAlias, skipUnavailable);
                    if (skipUnavailable) {
                        ActionListener.respondAndRelease(listener, SearchResponse.empty(timeProvider::buildTookInMillis, clusters));
                    } else {
                        listener.onFailure(wrapRemoteClusterFailure(clusterAlias, e));
                    }
                }
            });
        } else {
            SearchResponseMerger searchResponseMerger = createSearchResponseMerger(
                searchRequest.source(),
                timeProvider,
                aggReduceContextBuilder
            );
            task.setSearchResponseMergerSupplier(
                () -> createSearchResponseMerger(searchRequest.source(), timeProvider, aggReduceContextBuilder)
            );
            final AtomicReference<Exception> exceptions = new AtomicReference<>();
            int totalClusters = resolvedIndices.getRemoteClusterIndices().size() + (resolvedIndices.getLocalIndices() == null ? 0 : 1);
            final CountDown countDown = new CountDown(totalClusters);
            for (Map.Entry<String, OriginalIndices> entry : resolvedIndices.getRemoteClusterIndices().entrySet()) {
                String clusterAlias = entry.getKey();
                boolean skipUnavailable = remoteClusterService.isSkipUnavailable(clusterAlias);
                OriginalIndices indices = entry.getValue();
                SearchRequest ccsSearchRequest = SearchRequest.subSearchRequest(
                    parentTaskId,
                    searchRequest,
                    indices.indices(),
                    clusterAlias,
                    timeProvider.absoluteStartMillis(),
                    false
                );
                ActionListener<SearchResponse> ccsListener = createCCSListener(
                    clusterAlias,
                    skipUnavailable,
                    countDown,
                    exceptions,
                    searchResponseMerger,
                    clusters,
                    task.getProgressListener(),
                    listener
                );
                final var remoteClusterClient = remoteClusterService.getRemoteClusterClient(
                    clusterAlias,
                    remoteClientResponseExecutor,
                    RemoteClusterService.DisconnectedStrategy.RECONNECT_UNLESS_SKIP_UNAVAILABLE
                );
                remoteClusterClient.execute(TransportSearchAction.REMOTE_TYPE, ccsSearchRequest, ccsListener);
            }
            if (resolvedIndices.getLocalIndices() != null) {
                ActionListener<SearchResponse> ccsListener = createCCSListener(
                    RemoteClusterAware.LOCAL_CLUSTER_GROUP_KEY,
                    false,
                    countDown,
                    exceptions,
                    searchResponseMerger,
                    clusters,
                    task.getProgressListener(),
                    listener
                );
                SearchRequest ccsLocalSearchRequest = SearchRequest.subSearchRequest(
                    parentTaskId,
                    searchRequest,
                    resolvedIndices.getLocalIndices().indices(),
                    RemoteClusterAware.LOCAL_CLUSTER_GROUP_KEY,
                    timeProvider.absoluteStartMillis(),
                    false
                );
                localSearchConsumer.accept(ccsLocalSearchRequest, ccsListener);
            }
        }
    }

    static SearchResponseMerger createSearchResponseMerger(
        SearchSourceBuilder source,
        SearchTimeProvider timeProvider,
        AggregationReduceContext.Builder aggReduceContextBuilder
    ) {
        final int from;
        final int size;
        final int trackTotalHitsUpTo;
        if (source == null) {
            from = SearchService.DEFAULT_FROM;
            size = SearchService.DEFAULT_SIZE;
            trackTotalHitsUpTo = SearchContext.DEFAULT_TRACK_TOTAL_HITS_UP_TO;
        } else {
            from = source.from() == -1 ? SearchService.DEFAULT_FROM : source.from();
            size = source.size() == -1 ? SearchService.DEFAULT_SIZE : source.size();
            trackTotalHitsUpTo = source.trackTotalHitsUpTo() == null
                ? SearchContext.DEFAULT_TRACK_TOTAL_HITS_UP_TO
                : source.trackTotalHitsUpTo();
            // here we modify the original source so we can re-use it by setting it to each outgoing search request
            source.from(0);
            source.size(from + size);
        }
        return new SearchResponseMerger(from, size, trackTotalHitsUpTo, timeProvider, aggReduceContextBuilder);
    }

    /**
     * Collect remote search shards that we need to search for potential matches.
     * Used for ccs_minimize_roundtrips=false
     */
    static void collectSearchShards(
        IndicesOptions indicesOptions,
        String preference,
        String routing,
        QueryBuilder query,
        boolean allowPartialResults,
        SearchContextId searchContext,
        Map<String, OriginalIndices> remoteIndicesByCluster,
        SearchResponse.Clusters clusters,
        SearchTimeProvider timeProvider,
        TransportService transportService,
        ActionListener<Map<String, SearchShardsResponse>> listener
    ) {
        RemoteClusterService remoteClusterService = transportService.getRemoteClusterService();
        final CountDown responsesCountDown = new CountDown(remoteIndicesByCluster.size());
        final Map<String, SearchShardsResponse> searchShardsResponses = new ConcurrentHashMap<>();
        final AtomicReference<Exception> exceptions = new AtomicReference<>();
        for (Map.Entry<String, OriginalIndices> entry : remoteIndicesByCluster.entrySet()) {
            final String clusterAlias = entry.getKey();
            boolean skipUnavailable = remoteClusterService.isSkipUnavailable(clusterAlias);
            CCSActionListener<SearchShardsResponse, Map<String, SearchShardsResponse>> singleListener = new CCSActionListener<>(
                clusterAlias,
                skipUnavailable,
                responsesCountDown,
                exceptions,
                clusters,
                listener
            ) {
                @Override
                void innerOnResponse(SearchShardsResponse searchShardsResponse) {
                    assert ThreadPool.assertCurrentThreadPool(ThreadPool.Names.SEARCH_COORDINATION);
                    ccsClusterInfoUpdate(searchShardsResponse, clusters, clusterAlias, timeProvider);
                    searchShardsResponses.put(clusterAlias, searchShardsResponse);
                }

                @Override
                Map<String, SearchShardsResponse> createFinalResponse() {
                    return searchShardsResponses;
                }
            };
            remoteClusterService.maybeEnsureConnectedAndGetConnection(
                clusterAlias,
                skipUnavailable == false,
                singleListener.delegateFailureAndWrap((delegate, connection) -> {
                    final String[] indices = entry.getValue().indices();
                    final Executor responseExecutor = transportService.getThreadPool().executor(ThreadPool.Names.SEARCH_COORDINATION);
                    // TODO: support point-in-time
                    if (searchContext == null && connection.getTransportVersion().onOrAfter(TransportVersions.V_8_9_X)) {
                        SearchShardsRequest searchShardsRequest = new SearchShardsRequest(
                            indices,
                            indicesOptions,
                            query,
                            routing,
                            preference,
                            allowPartialResults,
                            clusterAlias
                        );
                        transportService.sendRequest(
                            connection,
                            TransportSearchShardsAction.TYPE.name(),
                            searchShardsRequest,
                            TransportRequestOptions.EMPTY,
                            new ActionListenerResponseHandler<>(delegate, SearchShardsResponse::new, responseExecutor)
                        );
                    } else {
                        // does not do a can-match
                        ClusterSearchShardsRequest searchShardsRequest = new ClusterSearchShardsRequest(
                            MasterNodeRequest.infiniteMasterNodeTimeout(connection.getTransportVersion()),
                            indices
                        ).indicesOptions(indicesOptions).local(true).preference(preference).routing(routing);
                        transportService.sendRequest(
                            connection,
                            TransportClusterSearchShardsAction.TYPE.name(),
                            searchShardsRequest,
                            TransportRequestOptions.EMPTY,
                            new ActionListenerResponseHandler<>(
                                delegate.map(SearchShardsResponse::fromLegacyResponse),
                                ClusterSearchShardsResponse::new,
                                responseExecutor
                            )
                        );
                    }
                })
            );
        }
    }

    /**
     * Only used for ccs_minimize_roundtrips=true pathway
     */
    private static ActionListener<SearchResponse> createCCSListener(
        String clusterAlias,
        boolean skipUnavailable,
        CountDown countDown,
        AtomicReference<Exception> exceptions,
        SearchResponseMerger searchResponseMerger,
        SearchResponse.Clusters clusters,
        SearchProgressListener progressListener,
        ActionListener<SearchResponse> originalListener
    ) {
        return new CCSActionListener<>(
            clusterAlias,
            skipUnavailable,
            countDown,
            exceptions,
            clusters,
            ActionListener.releaseAfter(originalListener, searchResponseMerger)
        ) {
            @Override
            void innerOnResponse(SearchResponse searchResponse) {
                ccsClusterInfoUpdate(searchResponse, clusters, clusterAlias, skipUnavailable);
                searchResponseMerger.add(searchResponse);
                progressListener.notifyClusterResponseMinimizeRoundtrips(clusterAlias, searchResponse);
            }

            @Override
            SearchResponse createFinalResponse() {
                return searchResponseMerger.getMergedResponse(clusters);
            }

            @Override
            protected void releaseResponse(SearchResponse searchResponse) {
                searchResponse.decRef();
            }
        };
    }

    /**
     * Creates a new Cluster object using the {@link ShardSearchFailure} info and skip_unavailable
     * flag to set Status. Then it swaps it in the clusters CHM at key clusterAlias
     */
    static void ccsClusterInfoUpdate(
        ShardSearchFailure failure,
        SearchResponse.Clusters clusters,
        String clusterAlias,
        boolean skipUnavailable
    ) {
        clusters.swapCluster(clusterAlias, (k, v) -> {
            SearchResponse.Cluster.Status status;
            if (skipUnavailable) {
                status = SearchResponse.Cluster.Status.SKIPPED;
            } else {
                status = SearchResponse.Cluster.Status.FAILED;
            }
            return new SearchResponse.Cluster.Builder(v).setStatus(status)
                .setFailures(CollectionUtils.appendToCopy(v.getFailures(), failure))
                .build();
        });
    }

    /**
     * Helper method common to multiple ccs_minimize_roundtrips=true code paths.
     * Used to update a specific SearchResponse.Cluster object state based upon
     * the SearchResponse coming from the cluster coordinator the search was performed on.
     * @param searchResponse SearchResponse from cluster sub-search
     * @param clusters Clusters that the search was executed on
     * @param clusterAlias Alias of the cluster to be updated
     */
    private static void ccsClusterInfoUpdate(
        SearchResponse searchResponse,
        SearchResponse.Clusters clusters,
        String clusterAlias,
        boolean skipUnavailable
    ) {
        /*
         * Cluster Status logic:
         * 1) FAILED if total_shards > 0 && all shards failed && skip_unavailable=false
         * 2) SKIPPED if total_shards > 0 && all shards failed && skip_unavailable=true
         * 3) PARTIAL if it timed out
         * 4) PARTIAL if it at least one of the shards succeeded but not all
         * 5) SUCCESSFUL if no shards failed (and did not time out)
         */
        clusters.swapCluster(clusterAlias, (k, v) -> {
            SearchResponse.Cluster.Status status;
            int totalShards = searchResponse.getTotalShards();
            if (totalShards > 0 && searchResponse.getFailedShards() >= totalShards) {
                if (skipUnavailable) {
                    status = SearchResponse.Cluster.Status.SKIPPED;
                } else {
                    status = SearchResponse.Cluster.Status.FAILED;
                }
            } else if (searchResponse.isTimedOut()) {
                status = SearchResponse.Cluster.Status.PARTIAL;
            } else if (searchResponse.getFailedShards() > 0) {
                status = SearchResponse.Cluster.Status.PARTIAL;
            } else {
                status = SearchResponse.Cluster.Status.SUCCESSFUL;
            }
            return new SearchResponse.Cluster.Builder(v).setStatus(status)
                .setTotalShards(totalShards)
                .setSuccessfulShards(searchResponse.getSuccessfulShards())
                .setSkippedShards(searchResponse.getSkippedShards())
                .setFailedShards(searchResponse.getFailedShards())
                .setFailures(Arrays.asList(searchResponse.getShardFailures()))
                .setTook(searchResponse.getTook())
                .setTimedOut(searchResponse.isTimedOut())
                .build();
        });
    }

    /**
     * Edge case ---
     * Typically we don't need to update a Cluster object after the SearchShards API call, since the
     * skipped shards will be passed into SearchProgressListener.onListShards.
     * However, there is an edge case where the remote SearchShards API call returns no shards at all.
     * So in that case, nothing for this cluster will be passed to onListShards, so we need to update
     * the Cluster object to SUCCESSFUL status with shard counts of 0 and a filled in 'took' value.
     *
     * @param response from SearchShards API call to remote cluster
     * @param clusters Clusters that the search was executed on
     * @param clusterAlias Alias of the cluster to be updated
     * @param timeProvider search time provider (for setting took value)
     */
    private static void ccsClusterInfoUpdate(
        SearchShardsResponse response,
        SearchResponse.Clusters clusters,
        String clusterAlias,
        SearchTimeProvider timeProvider
    ) {
        if (response.getGroups().isEmpty()) {
            clusters.swapCluster(
                clusterAlias,
                (k, v) -> new SearchResponse.Cluster.Builder(v).setStatus(SearchResponse.Cluster.Status.SUCCESSFUL)
                    .setTotalShards(0)
                    .setSuccessfulShards(0)
                    .setSkippedShards(0)
                    .setFailedShards(0)
                    .setFailures(Collections.emptyList())
                    .setTook(new TimeValue(timeProvider.buildTookInMillis()))
                    .setTimedOut(false)
                    .build()
            );
        }
    }

    void executeLocalSearch(
        Task task,
        SearchTimeProvider timeProvider,
        SearchRequest searchRequest,
        ResolvedIndices resolvedIndices,
        ClusterState clusterState,
        SearchResponse.Clusters clusterInfo,
        SearchPhaseProvider searchPhaseProvider
    ) {
        executeSearch(
            (SearchTask) task,
            timeProvider,
            searchRequest,
            resolvedIndices,
            Collections.emptyList(),
            (clusterName, nodeId) -> null,
            clusterState,
            Collections.emptyMap(),
            clusterInfo,
            searchPhaseProvider
        );
    }

    static BiFunction<String, String, DiscoveryNode> getRemoteClusterNodeLookup(Map<String, SearchShardsResponse> searchShardsResp) {
        Map<String, Map<String, DiscoveryNode>> clusterToNode = new HashMap<>();
        for (Map.Entry<String, SearchShardsResponse> entry : searchShardsResp.entrySet()) {
            String clusterAlias = entry.getKey();
            for (DiscoveryNode remoteNode : entry.getValue().getNodes()) {
                clusterToNode.computeIfAbsent(clusterAlias, k -> new HashMap<>()).put(remoteNode.getId(), remoteNode);
            }
        }
        return (clusterAlias, nodeId) -> {
            Map<String, DiscoveryNode> clusterNodes = clusterToNode.get(clusterAlias);
            if (clusterNodes == null) {
                throw new IllegalArgumentException("unknown remote cluster: " + clusterAlias);
            }
            return clusterNodes.get(nodeId);
        };
    }

    /**
     * Produce a list of {@link SearchShardIterator}s from the set of responses from remote clusters.
     * Used for ccs_minimize_roundtrips=false.
     */
    static List<SearchShardIterator> getRemoteShardsIterator(
        Map<String, SearchShardsResponse> searchShardsResponses,
        Map<String, OriginalIndices> remoteIndicesByCluster,
        Map<String, AliasFilter> aliasFilterMap
    ) {
        final List<SearchShardIterator> remoteShardIterators = new ArrayList<>();
        for (Map.Entry<String, SearchShardsResponse> entry : searchShardsResponses.entrySet()) {
            for (SearchShardsGroup searchShardsGroup : entry.getValue().getGroups()) {
                // add the cluster name to the remote index names for indices disambiguation
                // this ends up in the hits returned with the search response
                ShardId shardId = searchShardsGroup.shardId();
                AliasFilter aliasFilter = aliasFilterMap.get(shardId.getIndex().getUUID());
                String[] aliases = aliasFilter.getAliases();
                String clusterAlias = entry.getKey();
                String[] finalIndices = aliases.length == 0 ? new String[] { shardId.getIndexName() } : aliases;
                final OriginalIndices originalIndices = remoteIndicesByCluster.get(clusterAlias);
                assert originalIndices != null : "original indices are null for clusterAlias: " + clusterAlias;
                SearchShardIterator shardIterator = new SearchShardIterator(
                    clusterAlias,
                    shardId,
                    searchShardsGroup.allocatedNodes(),
                    new OriginalIndices(finalIndices, originalIndices.indicesOptions()),
                    null,
                    null,
                    searchShardsGroup.preFiltered(),
                    searchShardsGroup.skipped()
                );
                remoteShardIterators.add(shardIterator);
            }
        }
        return remoteShardIterators;
    }

    static List<SearchShardIterator> getRemoteShardsIteratorFromPointInTime(
        Map<String, SearchShardsResponse> searchShardsResponses,
        SearchContextId searchContextId,
        TimeValue searchContextKeepAlive,
        Map<String, OriginalIndices> remoteClusterIndices
    ) {
        final List<SearchShardIterator> remoteShardIterators = new ArrayList<>();
        for (Map.Entry<String, SearchShardsResponse> entry : searchShardsResponses.entrySet()) {
            for (SearchShardsGroup group : entry.getValue().getGroups()) {
                final ShardId shardId = group.shardId();
                final SearchContextIdForNode perNode = searchContextId.shards().get(shardId);
                if (perNode == null) {
                    // the shard was skipped after can match, hence it is not even part of the pit id
                    continue;
                }
                final String clusterAlias = entry.getKey();
                assert clusterAlias.equals(perNode.getClusterAlias()) : clusterAlias + " != " + perNode.getClusterAlias();
                final List<String> targetNodes = new ArrayList<>(group.allocatedNodes().size());
                if (perNode.getNode() != null) {
                    // If the shard was available when the PIT was created, it's included.
                    // Otherwise, we add the shard iterator without a target node, allowing a partial search failure to
                    // be thrown when a search phase attempts to access it.
                    targetNodes.add(perNode.getNode());
                    if (perNode.getSearchContextId().getSearcherId() != null) {
                        for (String node : group.allocatedNodes()) {
                            if (node.equals(perNode.getNode()) == false) {
                                targetNodes.add(node);
                            }
                        }
                    }
                }
                assert remoteClusterIndices.get(clusterAlias) != null : "original indices are null for clusterAlias: " + clusterAlias;
                final OriginalIndices finalIndices = new OriginalIndices(
                    new String[] { shardId.getIndexName() },
                    remoteClusterIndices.get(clusterAlias).indicesOptions()
                );
                SearchShardIterator shardIterator = new SearchShardIterator(
                    clusterAlias,
                    shardId,
                    targetNodes,
                    finalIndices,
                    perNode.getSearchContextId(),
                    searchContextKeepAlive,
                    false,
                    false
                );
                remoteShardIterators.add(shardIterator);
            }
        }
        assert checkAllRemotePITShardsWereReturnedBySearchShards(searchContextId.shards(), searchShardsResponses)
            : "search shards did not return remote shards that PIT included: " + searchContextId.shards();
        return remoteShardIterators;
    }

    private static boolean checkAllRemotePITShardsWereReturnedBySearchShards(
        Map<ShardId, SearchContextIdForNode> searchContextIdShards,
        Map<String, SearchShardsResponse> searchShardsResponses
    ) {
        Map<ShardId, SearchContextIdForNode> searchContextIdForNodeMap = new HashMap<>(searchContextIdShards);
        for (SearchShardsResponse searchShardsResponse : searchShardsResponses.values()) {
            for (SearchShardsGroup group : searchShardsResponse.getGroups()) {
                searchContextIdForNodeMap.remove(group.shardId());
            }
        }
        return searchContextIdForNodeMap.values()
            .stream()
            .allMatch(searchContextIdForNode -> searchContextIdForNode.getClusterAlias() == null);
    }

    /**
     * If any of the indices we are searching are frozen, issue deprecation warning.
     */
    void frozenIndexCheck(ResolvedIndices resolvedIndices) {
        List<String> frozenIndices = new ArrayList<>();
        Map<Index, IndexMetadata> indexMetadataMap = resolvedIndices.getConcreteLocalIndicesMetadata();
        for (var entry : indexMetadataMap.entrySet()) {
            if (entry.getValue().getSettings().getAsBoolean("index.frozen", false)) {
                frozenIndices.add(entry.getKey().getName());
            }
        }

        if (frozenIndices.isEmpty() == false) {
            DEPRECATION_LOGGER.warn(
                DeprecationCategory.INDICES,
                "search-frozen-indices",
                FROZEN_INDICES_DEPRECATION_MESSAGE,
                String.join(",", frozenIndices)
            );
        }
    }

    /**
     * Execute search locally and for all given remote shards.
     * Used when minimize_roundtrips=false or for local search.
     */
    private void executeSearch(
        SearchTask task,
        SearchTimeProvider timeProvider,
        SearchRequest searchRequest,
        ResolvedIndices resolvedIndices,
        List<SearchShardIterator> remoteShardIterators,
        BiFunction<String, String, DiscoveryNode> remoteConnections,
        ClusterState clusterState,
        Map<String, AliasFilter> remoteAliasMap,
        SearchResponse.Clusters clusters,
        SearchPhaseProvider searchPhaseProvider
    ) {
        if (searchRequest.allowPartialSearchResults() == null) {
            // No user preference defined in search request - apply cluster service default
            searchRequest.allowPartialSearchResults(searchService.defaultAllowPartialSearchResults());
        }

        // TODO: I think startTime() should become part of ActionRequest and that should be used both for index name
        // date math expressions and $now in scripts. This way all apis will deal with now in the same way instead
        // of just for the _search api
        final List<SearchShardIterator> localShardIterators;
        final Map<String, AliasFilter> aliasFilter;

        final String[] concreteLocalIndices;
        if (resolvedIndices.getSearchContextId() != null) {
            assert searchRequest.pointInTimeBuilder() != null;
            aliasFilter = resolvedIndices.getSearchContextId().aliasFilter();
            concreteLocalIndices = resolvedIndices.getLocalIndices() == null ? new String[0] : resolvedIndices.getLocalIndices().indices();
            localShardIterators = getLocalShardsIteratorFromPointInTime(
                clusterState,
                searchRequest.indicesOptions(),
                searchRequest.getLocalClusterAlias(),
                resolvedIndices.getSearchContextId(),
                searchRequest.pointInTimeBuilder().getKeepAlive(),
                searchRequest.allowPartialSearchResults()
            );
        } else {
            final Index[] indices = resolvedIndices.getConcreteLocalIndices();
            concreteLocalIndices = Arrays.stream(indices).map(Index::getName).toArray(String[]::new);
            final Set<String> indicesAndAliases = indexNameExpressionResolver.resolveExpressions(clusterState, searchRequest.indices());
            aliasFilter = buildIndexAliasFilters(clusterState, indicesAndAliases, indices);
            aliasFilter.putAll(remoteAliasMap);
            localShardIterators = getLocalShardsIterator(
                clusterState,
                searchRequest,
                searchRequest.getLocalClusterAlias(),
                indicesAndAliases,
                concreteLocalIndices
            );
        }
        final GroupShardsIterator<SearchShardIterator> shardIterators = mergeShardsIterators(localShardIterators, remoteShardIterators);

        failIfOverShardCountLimit(clusterService, shardIterators.size());

        if (searchRequest.getWaitForCheckpoints().isEmpty() == false) {
            if (remoteShardIterators.isEmpty() == false) {
                throw new IllegalArgumentException("Cannot use wait_for_checkpoints parameter with cross-cluster searches.");
            } else {
                validateAndResolveWaitForCheckpoint(clusterState, indexNameExpressionResolver, searchRequest, concreteLocalIndices);
            }
        }

        Map<String, Float> concreteIndexBoosts = resolveIndexBoosts(searchRequest, clusterState);

        adjustSearchType(searchRequest, shardIterators.size() == 1);

        final DiscoveryNodes nodes = clusterState.nodes();
        BiFunction<String, String, Transport.Connection> connectionLookup = buildConnectionLookup(
            searchRequest.getLocalClusterAlias(),
            nodes::get,
            remoteConnections,
            searchTransportService::getConnection
        );
        final Executor asyncSearchExecutor = asyncSearchExecutor(concreteLocalIndices);
        final boolean preFilterSearchShards = shouldPreFilterSearchShards(
            clusterState,
            searchRequest,
            concreteLocalIndices,
            localShardIterators.size() + remoteShardIterators.size(),
            defaultPreFilterShardSize
        );
        searchPhaseProvider.newSearchPhase(
            task,
            searchRequest,
            asyncSearchExecutor,
            shardIterators,
            timeProvider,
            connectionLookup,
            clusterState,
            Collections.unmodifiableMap(aliasFilter),
            concreteIndexBoosts,
            preFilterSearchShards,
            threadPool,
            clusters
        ).start();
    }

    Executor asyncSearchExecutor(final String[] indices) {
        final List<String> executorsForIndices = Arrays.stream(indices).map(executorSelector::executorForSearch).toList();
        if (executorsForIndices.size() == 1) { // all indices have same executor
            return threadPool.executor(executorsForIndices.get(0));
        }
        if (executorsForIndices.size() == 2
            && executorsForIndices.contains(SYSTEM_READ)
            && executorsForIndices.contains(SYSTEM_CRITICAL_READ)) { // mix of critical and non critical system indices
            return threadPool.executor(SYSTEM_READ);
        }
        return threadPool.executor(ThreadPool.Names.SEARCH);
    }

    static BiFunction<String, String, Transport.Connection> buildConnectionLookup(
        String requestClusterAlias,
        Function<String, DiscoveryNode> localNodes,
        BiFunction<String, String, DiscoveryNode> remoteNodes,
        BiFunction<String, DiscoveryNode, Transport.Connection> nodeToConnection
    ) {
        return (clusterAlias, nodeId) -> {
            final DiscoveryNode discoveryNode;
            final boolean remoteCluster;
            if (clusterAlias == null || requestClusterAlias != null) {
                assert requestClusterAlias == null || requestClusterAlias.equals(clusterAlias);
                discoveryNode = localNodes.apply(nodeId);
                remoteCluster = false;
            } else {
                discoveryNode = remoteNodes.apply(clusterAlias, nodeId);
                remoteCluster = true;
            }
            if (discoveryNode == null) {
                throw new IllegalStateException("no node found for id: " + nodeId);
            }
            return nodeToConnection.apply(remoteCluster ? clusterAlias : null, discoveryNode);
        };
    }

    static boolean shouldPreFilterSearchShards(
        ClusterState clusterState,
        SearchRequest searchRequest,
        String[] indices,
        int numShards,
        int defaultPreFilterShardSize
    ) {
        if (searchRequest.searchType() != QUERY_THEN_FETCH) {
            // we can't do this for DFS it needs to fan out to all shards all the time
            return false;
        }
        SearchSourceBuilder source = searchRequest.source();
        Integer preFilterShardSize = searchRequest.getPreFilterShardSize();
        if (preFilterShardSize == null) {
            if (hasReadOnlyIndices(indices, clusterState) || hasPrimaryFieldSort(source)) {
                preFilterShardSize = 1;
            } else {
                preFilterShardSize = defaultPreFilterShardSize;
            }
        }
        return preFilterShardSize < numShards && (SearchService.canRewriteToMatchNone(source) || hasPrimaryFieldSort(source));
    }

    private static boolean hasReadOnlyIndices(String[] indices, ClusterState clusterState) {
        var blocks = clusterState.blocks();
        if (blocks.global().isEmpty() && blocks.indices().isEmpty()) {
            // short circuit optimization because block check below is relatively expensive for many indices
            return false;
        }
        for (String index : indices) {
            ClusterBlockException writeBlock = blocks.indexBlockedException(ClusterBlockLevel.WRITE, index);
            if (writeBlock != null) {
                return true;
            }
        }
        return false;
    }

    // package private for testing
    static GroupShardsIterator<SearchShardIterator> mergeShardsIterators(
        List<SearchShardIterator> localShardIterators,
        List<SearchShardIterator> remoteShardIterators
    ) {
        final List<SearchShardIterator> shards;
        if (remoteShardIterators.isEmpty()) {
            shards = localShardIterators;
        } else {
            shards = CollectionUtils.concatLists(remoteShardIterators, localShardIterators);
        }
        return GroupShardsIterator.sortAndCreate(shards);
    }

    interface SearchPhaseProvider {
        SearchPhase newSearchPhase(
            SearchTask task,
            SearchRequest searchRequest,
            Executor executor,
            GroupShardsIterator<SearchShardIterator> shardIterators,
            SearchTimeProvider timeProvider,
            BiFunction<String, String, Transport.Connection> connectionLookup,
            ClusterState clusterState,
            Map<String, AliasFilter> aliasFilter,
            Map<String, Float> concreteIndexBoosts,
            boolean preFilter,
            ThreadPool threadPool,
            SearchResponse.Clusters clusters
        );
    }

    private class AsyncSearchActionProvider implements SearchPhaseProvider {
        private final ActionListener<SearchResponse> listener;

        AsyncSearchActionProvider(ActionListener<SearchResponse> listener) {
            this.listener = listener;
        }

        @Override
        public SearchPhase newSearchPhase(
            SearchTask task,
            SearchRequest searchRequest,
            Executor executor,
            GroupShardsIterator<SearchShardIterator> shardIterators,
            SearchTimeProvider timeProvider,
            BiFunction<String, String, Transport.Connection> connectionLookup,
            ClusterState clusterState,
            Map<String, AliasFilter> aliasFilter,
            Map<String, Float> concreteIndexBoosts,
            boolean preFilter,
            ThreadPool threadPool,
            SearchResponse.Clusters clusters
        ) {
            if (preFilter) {
                return new CanMatchPreFilterSearchPhase(
                    logger,
                    searchTransportService,
                    connectionLookup,
                    aliasFilter,
                    concreteIndexBoosts,
                    threadPool.executor(ThreadPool.Names.SEARCH_COORDINATION),
                    searchRequest,
                    shardIterators,
                    timeProvider,
                    task,
                    true,
                    searchService.getCoordinatorRewriteContextProvider(timeProvider::absoluteStartMillis),
                    listener.delegateFailureAndWrap(
                        (l, iters) -> newSearchPhase(
                            task,
                            searchRequest,
                            executor,
                            iters,
                            timeProvider,
                            connectionLookup,
                            clusterState,
                            aliasFilter,
                            concreteIndexBoosts,
                            false,
                            threadPool,
                            clusters
                        ).start()
                    )
                );
            }
            // for synchronous CCS minimize_roundtrips=false, use the CCSSingleCoordinatorSearchProgressListener
            // (AsyncSearchTask will not return SearchProgressListener.NOOP, since it uses its own progress listener
            // which delegates to CCSSingleCoordinatorSearchProgressListener when minimizing roundtrips)
            if (clusters.isCcsMinimizeRoundtrips() == false
                && clusters.hasRemoteClusters()
                && task.getProgressListener() == SearchProgressListener.NOOP) {
                task.setProgressListener(new CCSSingleCoordinatorSearchProgressListener());
            }
            final SearchPhaseResults<SearchPhaseResult> queryResultConsumer = searchPhaseController.newSearchPhaseResults(
                executor,
                circuitBreaker,
                task::isCancelled,
                task.getProgressListener(),
                searchRequest,
                shardIterators.size(),
                exc -> searchTransportService.cancelSearchTask(task, "failed to merge result [" + exc.getMessage() + "]")
            );
            boolean success = false;
            try {
                final SearchPhase searchPhase;
                if (searchRequest.searchType() == DFS_QUERY_THEN_FETCH) {
                    searchPhase = new SearchDfsQueryThenFetchAsyncAction(
                        logger,
                        namedWriteableRegistry,
                        searchTransportService,
                        connectionLookup,
                        aliasFilter,
                        concreteIndexBoosts,
                        executor,
                        queryResultConsumer,
                        searchRequest,
                        listener,
                        shardIterators,
                        timeProvider,
                        clusterState,
                        task,
                        clusters,
                        client
                    );
                } else {
                    assert searchRequest.searchType() == QUERY_THEN_FETCH : searchRequest.searchType();
                    searchPhase = new SearchQueryThenFetchAsyncAction(
                        logger,
                        namedWriteableRegistry,
                        searchTransportService,
                        connectionLookup,
                        aliasFilter,
                        concreteIndexBoosts,
                        executor,
                        queryResultConsumer,
                        searchRequest,
                        listener,
                        shardIterators,
                        timeProvider,
                        clusterState,
                        task,
                        clusters,
                        client
                    );
                }
                success = true;
                return searchPhase;
            } finally {
                if (success == false) {
                    queryResultConsumer.close();
                }
            }
        }
    }

    private static void validateAndResolveWaitForCheckpoint(
        ClusterState clusterState,
        IndexNameExpressionResolver resolver,
        SearchRequest searchRequest,
        String[] concreteLocalIndices
    ) {
        HashSet<String> searchedIndices = new HashSet<>(Arrays.asList(concreteLocalIndices));
        Map<String, long[]> newWaitForCheckpoints = Maps.newMapWithExpectedSize(searchRequest.getWaitForCheckpoints().size());
        for (Map.Entry<String, long[]> waitForCheckpointIndex : searchRequest.getWaitForCheckpoints().entrySet()) {
            long[] checkpoints = waitForCheckpointIndex.getValue();
            int checkpointsProvided = checkpoints.length;
            String target = waitForCheckpointIndex.getKey();
            Index resolved;
            try {
                resolved = resolver.concreteSingleIndex(clusterState, new IndicesRequest() {
                    @Override
                    public String[] indices() {
                        return new String[] { target };
                    }

                    @Override
                    public IndicesOptions indicesOptions() {
                        return IndicesOptions.strictSingleIndexNoExpandForbidClosed();
                    }
                });
            } catch (Exception e) {
                throw new IllegalArgumentException(
                    "Failed to resolve wait_for_checkpoints target ["
                        + target
                        + "]. Configured target "
                        + "must resolve to a single open index.",
                    e
                );
            }
            String index = resolved.getName();
            IndexMetadata indexMetadata = clusterState.metadata().index(index);
            if (searchedIndices.contains(index) == false) {
                throw new IllegalArgumentException(
                    "Target configured with wait_for_checkpoints must be a concrete index resolved in "
                        + "this search. Target ["
                        + target
                        + "] is not a concrete index resolved in this search."
                );
            } else if (indexMetadata == null) {
                throw new IllegalArgumentException("Cannot find index configured for wait_for_checkpoints parameter [" + index + "].");
            } else if (indexMetadata.getNumberOfShards() != checkpointsProvided) {
                throw new IllegalArgumentException(
                    "Target configured with wait_for_checkpoints must search the same number of shards as "
                        + "checkpoints provided. ["
                        + checkpointsProvided
                        + "] checkpoints provided. Target ["
                        + target
                        + "] which resolved to "
                        + "index ["
                        + index
                        + "] has "
                        + "["
                        + indexMetadata.getNumberOfShards()
                        + "] shards."
                );
            }
            newWaitForCheckpoints.put(index, checkpoints);
        }
        searchRequest.setWaitForCheckpoints(Collections.unmodifiableMap(newWaitForCheckpoints));
    }

    private static void failIfOverShardCountLimit(ClusterService clusterService, int shardCount) {
        final long shardCountLimit = clusterService.getClusterSettings().get(SHARD_COUNT_LIMIT_SETTING);
        if (shardCount > shardCountLimit) {
            throw new IllegalArgumentException(
                "Trying to query "
                    + shardCount
                    + " shards, which is over the limit of "
                    + shardCountLimit
                    + ". This limit exists because querying many shards at the same time can make the "
                    + "job of the coordinating node very CPU and/or memory intensive. It is usually a better idea to "
                    + "have a smaller number of larger shards. Update ["
                    + SHARD_COUNT_LIMIT_SETTING.getKey()
                    + "] to a greater value if you really want to query that many shards at the same time."
            );
        }
    }

    /**
     * {@link ActionListener} suitable for collecting cross-cluster responses.
     * @param <Response> Response type we're getting as intermediate per-cluster results.
     * @param <FinalResponse> Response type that the final listener expects.
     */
    abstract static class CCSActionListener<Response, FinalResponse> implements ActionListener<Response> {
        protected final String clusterAlias;
        protected final boolean skipUnavailable;
        private final CountDown countDown;
        private final AtomicReference<Exception> exceptions;
        protected final SearchResponse.Clusters clusters;
        private final ActionListener<FinalResponse> originalListener;

        /**
         * Used by both minimize_roundtrips true and false
         */
        CCSActionListener(
            String clusterAlias,
            boolean skipUnavailable,
            CountDown countDown,
            AtomicReference<Exception> exceptions,
            SearchResponse.Clusters clusters,
            ActionListener<FinalResponse> originalListener
        ) {
            this.clusterAlias = clusterAlias;
            this.skipUnavailable = skipUnavailable;
            this.countDown = countDown;
            this.exceptions = exceptions;
            this.clusters = clusters;
            this.originalListener = originalListener;
        }

        @Override
        public final void onResponse(Response response) {
            innerOnResponse(response);
            maybeFinish();
        }

        /**
         * Specific listener type will implement this method to process its specific partial response.
         */
        abstract void innerOnResponse(Response response);

        @Override
        public final void onFailure(Exception e) {
            ShardSearchFailure f = new ShardSearchFailure(e);
            logCCSError(f, clusterAlias, skipUnavailable);
            SearchResponse.Cluster cluster = clusters.getCluster(clusterAlias);
            if (skipUnavailable) {
                if (cluster != null) {
                    ccsClusterInfoUpdate(f, clusters, clusterAlias, true);
                }
            } else {
                if (cluster != null) {
                    ccsClusterInfoUpdate(f, clusters, clusterAlias, false);
                }
                Exception exception = e;
                if (RemoteClusterAware.LOCAL_CLUSTER_GROUP_KEY.equals(clusterAlias) == false) {
                    exception = wrapRemoteClusterFailure(clusterAlias, e);
                }
                if (exceptions.compareAndSet(null, exception) == false) {
                    exceptions.accumulateAndGet(exception, (previous, current) -> {
                        current.addSuppressed(previous);
                        return current;
                    });
                }
            }
            maybeFinish();
        }

        private void maybeFinish() {
            if (countDown.countDown()) {
                Exception exception = exceptions.get();
                if (exception == null) {
                    FinalResponse response;
                    try {
                        response = createFinalResponse();
                    } catch (Exception e) {
                        originalListener.onFailure(e);
                        return;
                    }
                    try {
                        originalListener.onResponse(response);
                    } finally {
                        releaseResponse(response);
                    }
                } else {
                    originalListener.onFailure(exceptions.get());
                }
            }
        }

        protected void releaseResponse(FinalResponse response) {}

        abstract FinalResponse createFinalResponse();
    }

    /**
     * In order to gather data on what types of CCS errors happen in the field, we will log
     * them using the ShardSearchFailure XContent (JSON), which supplies information about underlying
     * causes of shard failures.
     * @param f ShardSearchFailure to log
     * @param clusterAlias cluster on which the failure occurred
     * @param skipUnavailable the skip_unavailable setting of the cluster with the search error
     */
    private static void logCCSError(ShardSearchFailure f, String clusterAlias, boolean skipUnavailable) {
        String errorInfo;
        try {
            errorInfo = Strings.toString(f.toXContent(XContentFactory.jsonBuilder(), ToXContent.EMPTY_PARAMS));
        } catch (IOException ex) {
            // use the toString as a fallback if for some reason the XContent conversion to JSON fails
            errorInfo = f.toString();
        }
        logger.debug(
            "CCS remote cluster failure. Cluster [{}]. skip_unavailable: [{}]. Error: {}",
            clusterAlias,
            skipUnavailable,
            errorInfo
        );
    }

    private static RemoteTransportException wrapRemoteClusterFailure(String clusterAlias, Exception e) {
        return new RemoteTransportException("error while communicating with remote cluster [" + clusterAlias + "]", e);
    }

    static List<SearchShardIterator> getLocalShardsIteratorFromPointInTime(
        ClusterState clusterState,
        IndicesOptions indicesOptions,
        String localClusterAlias,
        SearchContextId searchContext,
        TimeValue keepAlive,
        boolean allowPartialSearchResults
    ) {
        final List<SearchShardIterator> iterators = new ArrayList<>(searchContext.shards().size());
        for (Map.Entry<ShardId, SearchContextIdForNode> entry : searchContext.shards().entrySet()) {
            final SearchContextIdForNode perNode = entry.getValue();
            if (Strings.isEmpty(perNode.getClusterAlias())) {
                final ShardId shardId = entry.getKey();
                final List<String> targetNodes = new ArrayList<>(2);
                if (perNode.getNode() != null) {
                    // If the shard was available when the PIT was created, it's included.
                    // Otherwise, we add the shard iterator without a target node, allowing a partial search failure to
                    // be thrown when a search phase attempts to access it.
                    try {
                        final ShardIterator shards = OperationRouting.getShards(clusterState, shardId);
                        // Prefer executing shard requests on nodes that are part of PIT first.
                        if (clusterState.nodes().nodeExists(perNode.getNode())) {
                            targetNodes.add(perNode.getNode());
                        }
                        if (perNode.getSearchContextId().getSearcherId() != null) {
                            for (ShardRouting shard : shards) {
                                if (shard.currentNodeId().equals(perNode.getNode()) == false) {
                                    targetNodes.add(shard.currentNodeId());
                                }
                            }
                        }
                    } catch (IndexNotFoundException | ShardNotFoundException e) {
                        // We can hit these exceptions if the index was deleted after creating PIT or the cluster state on
                        // this coordinating node is outdated. It's fine to ignore these extra "retry-able" target shards
                        // when allowPartialSearchResults is false
                        if (allowPartialSearchResults == false) {
                            throw e;
                        }
                    }
                }
                OriginalIndices finalIndices = new OriginalIndices(new String[] { shardId.getIndexName() }, indicesOptions);
                iterators.add(
                    new SearchShardIterator(
                        localClusterAlias,
                        shardId,
                        targetNodes,
                        finalIndices,
                        perNode.getSearchContextId(),
                        keepAlive,
                        false,
                        false
                    )
                );
            }
        }
        return iterators;
    }

    /**
     * Create a list of {@link SearchShardIterator}s for the local indices we are searching.
     * This resolves aliases and index expressions.
     */
    List<SearchShardIterator> getLocalShardsIterator(
        ClusterState clusterState,
        SearchRequest searchRequest,
        String clusterAlias,
        Set<String> indicesAndAliases,
        String[] concreteIndices
    ) {
        var routingMap = indexNameExpressionResolver.resolveSearchRouting(clusterState, searchRequest.routing(), searchRequest.indices());
        GroupShardsIterator<ShardIterator> shardRoutings = clusterService.operationRouting()
            .searchShards(
                clusterState,
                concreteIndices,
                routingMap,
                searchRequest.preference(),
                searchService.getResponseCollectorService(),
                searchTransportService.getPendingSearchRequests()
            );
        final Map<String, OriginalIndices> originalIndices = buildPerIndexOriginalIndices(
            clusterState,
            indicesAndAliases,
            concreteIndices,
            searchRequest.indicesOptions()
        );
        SearchShardIterator[] list = new SearchShardIterator[shardRoutings.size()];
        int i = 0;
        for (ShardIterator shardRouting : shardRoutings) {
            final ShardId shardId = shardRouting.shardId();
            OriginalIndices finalIndices = originalIndices.get(shardId.getIndex().getName());
            assert finalIndices != null;
            list[i++] = new SearchShardIterator(clusterAlias, shardId, shardRouting.getShardRoutings(), finalIndices);
        }
        // the returned list must support in-place sorting, so this is the most memory efficient we can do here
        return Arrays.asList(list);
    }

    private interface TelemetryListener {
        void setRemotes(int count);

        void setFeature(String feature);

        void setClient(String client);
    }

    private class SearchResponseActionListener implements ActionListener<SearchResponse>, TelemetryListener {
        private final SearchTask task;
        private final ActionListener<SearchResponse> listener;
        private final CCSUsage.Builder usageBuilder;

        SearchResponseActionListener(SearchTask task, ActionListener<SearchResponse> listener) {
            this.task = task;
            this.listener = listener;
            usageBuilder = new CCSUsage.Builder();
        }

        /**
         * Should we collect telemetry for this search?
         */
        private boolean collectTelemetry() {
            return CCS_TELEMETRY_FEATURE_FLAG.isEnabled() && usageBuilder.getRemotesCount() > 0;
        }

        public void setRemotes(int count) {
            usageBuilder.setRemotesCount(count);
        }

        @Override
        public void setFeature(String feature) {
            usageBuilder.setFeature(feature);
        }

        @Override
        public void setClient(String client) {
            usageBuilder.setClient(client);
        }

        @Override
        public void onResponse(SearchResponse searchResponse) {
            try {
                searchResponseMetrics.recordTookTime(searchResponse.getTookInMillis());
                SearchResponseMetrics.ResponseCountTotalStatus responseCountTotalStatus =
                    SearchResponseMetrics.ResponseCountTotalStatus.SUCCESS;
                if (searchResponse.getShardFailures() != null && searchResponse.getShardFailures().length > 0) {
                    // Deduplicate failures by exception message and index
                    ShardOperationFailedException[] groupedFailures = ExceptionsHelper.groupBy(searchResponse.getShardFailures());
                    for (ShardOperationFailedException f : groupedFailures) {
                        boolean causeHas500Status = false;
                        if (f.getCause() != null) {
                            causeHas500Status = ExceptionsHelper.status(f.getCause()).getStatus() >= 500;
                        }
                        if ((f.status().getStatus() >= 500 || causeHas500Status)
                            && ExceptionsHelper.isNodeOrShardUnavailableTypeException(f.getCause()) == false) {
                            logger.warn("TransportSearchAction shard failure (partial results response)", f);
                            responseCountTotalStatus = SearchResponseMetrics.ResponseCountTotalStatus.PARTIAL_FAILURE;
                        }
                    }
                }
                searchResponseMetrics.incrementResponseCount(responseCountTotalStatus);

                if (collectTelemetry()) {
                    extractCCSTelemetry(searchResponse);
                    recordTelemetry();
                }
            } catch (Exception e) {
                onFailure(e);
                return;
            }
            // This is last because we want to collect telemetry before returning the response.
            listener.onResponse(searchResponse);
        }

        @Override
        public void onFailure(Exception e) {
            searchResponseMetrics.incrementResponseCount(SearchResponseMetrics.ResponseCountTotalStatus.FAILURE);
            if (collectTelemetry()) {
                usageBuilder.setFailure(e);
                recordTelemetry();
            }
            listener.onFailure(e);
        }

        private void recordTelemetry() {
            usageService.getCcsUsageHolder().updateUsage(usageBuilder.build());
        }

        /**
         * Extract telemetry data from the search response.
         * @param searchResponse The final response from the search.
         */
        private void extractCCSTelemetry(SearchResponse searchResponse) {
            usageBuilder.took(searchResponse.getTookInMillis());
            for (String clusterAlias : searchResponse.getClusters().getClusterAliases()) {
                SearchResponse.Cluster cluster = searchResponse.getClusters().getCluster(clusterAlias);
                if (cluster.getStatus() == SearchResponse.Cluster.Status.SKIPPED) {
                    usageBuilder.skippedRemote(clusterAlias);
                } else {
                    usageBuilder.perClusterUsage(clusterAlias, cluster.getTook());
                }
            }

        }

    }
}
